Contradiction with John 1:18
This verse says no one has seen God at any time, while Mark 9:8 describes a vision of Jesus, suggesting a divine experience.
John 1:18: No man hath seen God at any time; the only begotten Son, which is in the bosom of the Father, he hath declared [him].
Contradiction with 1 Timothy 6:16
This verse declares that God dwells in unapproachable light and cannot be seen, contradicting the disciples' vision in Mark 9:8.
1 Timothy 6:16: Who only hath immortality, dwelling in the light which no man can approach unto; whom no man hath seen, nor can see: to whom [be] honour and power everlasting. Amen.
Contradiction with Exodus 33:20
God tells Moses that no man can see Him and live, contradicting the disciples' experience in Mark 9:8 where they see Jesus transfigured.
Exodus 33:20: And he said, Thou canst not see my face: for there shall no man see me, and live.
Contradiction with Isaiah 6:1
Isaiah claims to have seen the Lord sitting upon a throne, which contrasts the notion in Mark 9:8 about the disciples seeing no one but Jesus only.
Isaiah 6:1: In the year that king Uzziah died I saw also the Lord sitting upon a throne, high and lifted up, and his train filled the temple. [his...: or, the skirts thereof]